PK/PD modeling of 5-hydroxytryptophan (5-HTP) challenge test with cortisol measurement in serum and saliva

This research was planned to build a Pharmacokinetic/Pharmacodynamic (PK/PD) model of 5‐hydroxytryptophan (5‐HTP) challenge study including a circadian rhythm component of cortisol and to predict serum cortisol based on saliva cortisol. Data from three 5‐HTP challenge studies in healthy volunteers were collected. Serum 5‐HTP, saliva, and serum cortisol were sampled as PK and PD marker. The population PK/PD modeling approach was applied. A baseline model of serum cortisol was built to assess the circadian rhythm before a pharmacodynamic model was used to evaluate the drug effect of the 5‐HTP on cortisol. Finally, linear and power function relationships were tested to predict serum cortisol based on saliva cortisol. The PK of 5‐HTP could be described using a one‐compartment model with a transit compartment. The typical value for clearance was 20.40 L h⁻¹ and showed inter‐study variability. A cosine function was chosen and properly described the circadian rhythm of serum cortisol. A linear approximation model was applied to fit the 5‐HTP PD effect on cortisol data with a slope of 4.16 ng mL⁻¹ h. A power function provided a better description than a linear function to relate the saliva and serum cortisol. In conclusion, a circadian rhythm component was built in the PK/PD model of the 5‐HTP challenge test which could better improve the understanding of the stimulating effect on HPA with cortisol change. After the 5‐HTP challenge, saliva cortisol correlated well with serum cortisol and was predictable by a population PK‐PD model.

Central nervous system effects of alcohol at a pseudo-steady-state concentration using alcohol clamping in healthy volunteers

AIM

In determining the acute effects of alcohol, it is helpful if alcohol concentrations are maintained at stable levels, to facilitate the interpretation of the results. Recently, an alcohol clamping method was developed that resulted in stable alcohol concentrations for hours. The aim of this study was to test a range of central nervous system (CNS) effects under pseudo-steady-state conditions.

METHODS

To achieve a pseudo-steady state of 0.6 g l(-1), breath alcohol concentrations (BrAC) were frequently measured and fed back into a spreadsheet-based program to guide intravenous dosing. CNS effects were frequently measured throughout the clamp.

RESULTS

The clamping paradigm resulted in a pseudo-steady-state BrAC of 0.61 g l(-1) (coefficient of variation 6.2%). A plateau was maintained from 25 to 300 min and caused significant effects on smooth pursuit eye movements [-9.7%, 95% confidence interval (CI) -12.4, -7.1], adaptive tracking (-3.4%, 95% CI -4.5, -2.2), visual analogue scale (VAS) alertness (-13 mm, 95% CI -20, -6), VAS alcohol effects (16 mm, 95% CI 7, 25) and body sway (21.3%, 95% CI 1.8, 45). Some effects (like smooth pursuit eye movements) closely followed the relatively stable alcohol concentrations, whereas others (such as body sway and VAS alcohol effects) fluctuated during the plateau phase.

CONCLUSIONS

Most CNS effects of alcohol showed a trend to change over time, despite stable concentrations. Other variables remained stable under pseudo-steady-state conditions. The intravenous clamping method provides precise control over BrAC levels and allows frequent repetition of different CNS measurements. These features make this technique eminently suitable to study the complex pharmacodynamic effects of acute alcohol administration.

Explaining variability in ciclosporin exposure in adult kidney transplant recipients

Purpose

Optimal ciclosporin A (CsA) exposure in kidney transplant recipients is difficult to attain because of variability in CsA pharmacokinetics. A better understanding of the variability in CsA exposure could be a good means of individualizing therapy. Specifically, genetic variability in genes involved in CsA metabolism could explain exposure differences. Therefore, this study is aimed at identifying a relationship between genetic polymorphisms and the variability in CsA exposure, while accounting for non-genetic sources of variability.

Methods

De novo kidney transplant patients (n = 33) were treated with CsA for 1 year and extensive blood sampling was performed on multiple occasions throughout the year. The effects of the non-genetic covariates hematocrit, serum albumin concentration, cholesterol, demographics (i.e., body weight), CsA dose interval, prednisolone dose and genetic polymorphisms in genes encoding ABCB1, CYP3A4, CYP3A5, and PXR on CsA pharmacokinetics were studied using non-linear mixed effect modeling.

Results

The pharmacokinetics of CsA were described by a two-compartment disposition model with delayed absorption. Body weight was identified as the most important covariate and explained 35% of the random inter-individual variability in CsA clearance. Moreover, concurrent prednisolone use at a dosage of 20 mg/day or higher was associated with a 22% higher clearance of CsA, hence lower CsA exposure. In contrast, no considerable genotype effects (i.e., greater than 30–50%) on CsA clearance were found for the selected genes.

Conclusions

It appears that the selected genetic markers explain variability in CsA exposure insufficiently to be of clinical relevance. Therefore, therapeutic drug monitoring is still required to optimize CsA exposure after administration of individualized doses based on body weight and, as this study suggests, co-administration of prednisolone.

Noninvasive functional liver blood flow measurement: comparison between bolus dose and steady-state clearance of sorbitol in a small-rodent model

Plasma clearance of D-sorbitol, a nontoxic polyol, occurs predominantly in the liver and has been used to measure functional liver blood flow after bolus and steady- state intravenous administration. However, it is not known which of these two administration methods is superior. Therefore, plasma D-sorbitol clearance was studied in an animal model both after a bolus dose and under steady-state (SS) conditions and compared directly with liver blood flow, under normal conditions, and after the induction of endotoxin (LPS) sepsis. Adult male Wistar rats (526 +/- 38 g body wt; n = 27) were anesthetized and mechanically ventilated. Hemodynamics, hepatic arterial flow, and portal venous flow were measured. Two groups were studied, namely healthy animals that served as controls and a sepsis group that received 5 mg/kg LPS intravenously (Escherichia coli O127:B8). Each animal received either a SS infusion (0.1 mg/100 g body wt per min) or a bolus (3 mg/100 g body wt) of a 5% D-sorbitol solution intravenously in a randomized order. After the initial measurements and a 60-min pause time in between (T(1/2,sorbitol) = 9 min), a crossover was done. The hepatic clearance of D-sorbitol in the control group showed a good correlation between bolus and SS (Spearman's r = 0.7681, P = 0.0004), and both techniques correlated well with total liver blood flow (TLBF) (r = 0.7239, P = 0.0023 and r = 0.7226, P = 0.0023, respectively). Also in the sepsis group there was a good correlation between bolus and SS sorbitol clearance (r = 0.6655, P = 0.0182). In the sepsis group, only the SS clearance correlated with TLBF (r = 0.6434, P = 0.024). In conclusion, in normal and under septic conditions, hepatic clearance of D-sorbitol either by bolus or a SS infusion is comparable. In healthy animals, this also correlated well with TLBF but not in septic conditions. However, this is expected because of the changes in the liver microcirculation, shunting, and decreased hepatocyte function in sepsis.

Increased melanogenesis is a risk factor for oxidative DNA damage--study on cultured melanocytes and atypical nevus cells

Melanin synthesis is an oxygen-dependent process that acts as a potential source of reactive oxygen species (ROS) inside pigment-forming cells. The synthesis of the lighter variant of melanin, pheomelanin, consumes cysteine and this may limit the capacity of the cellular antioxidative defense. We show that tyrosine-induced melanogenesis in cultured normal human melanocytes (NHM) is accompanied by increased production of ROS and decreased concentration of intracellular glutathione. Clinical atypical (dysplastic) nevi (DN) regularly contain more melanin than do normal melanocytes (MC). We also show that in these cultured DN cells three out of four exhibit elevated synthesis of pheomelanin and this is accompanied by their early senescence. By using various redox-sensitive molecular probes, we demonstrate that cultured DN cells produce significantly more ROS than do normal MC from the same donor. Our experiments employing single-cell gel electrophoresis (comet assay) usually reveal higher fragmentation of DNA in DN cells than in normal MC. Even if in some cases the normal alkaline comet assay shows no differences in DNA fragmentation between DN cells and normal MC, the use of the comet assay with formamidopyrimidine DNA glycosylase can disclose that the DNA of the cultured DN cells harbor more oxidative damage than the DNA of normal MC from the same person.